Some internal combustion engines employ a particulate filter in an exhaust system to trap particulate matter flowing through the exhaust system and thereby meet emission standards. A turbocharged, spark-ignition engine may employ a particle filter to trap soot, for example. As particulate matter accumulates in a particulate filter, exhaust backpressure will increase, which can adversely affect fuel economy. Accordingly, a particulate filter may be periodically regenerated by oxidizing stored particulate matter. A regeneration reaction requires oxygen and suitable temperature conditions. Supplying excess oxygen for a regeneration reaction in a spark-ignition may be difficult, however, as spark-ignition engines are typically operated under stoichiometric conditions.
U.S. Patent Application No. 2011/0073088 discloses methods of regenerating a particulate filter in a spark-ignition engine. In one example, deceleration fuel shut-off (DFSO) is utilized to supply excess oxygen to a particulate filter and thereby facilitate regeneration of the filter. Passive filter regeneration is also described in which soot stored in a filter may be oxidized without explicitly modifying engine operation to increase the supply of excess oxygen to the filter.
The inventors herein have recognized an issue with the approach identified above. Excess oxygen supplied to a particulate filter for a regeneration reaction during DFSO may be completely consumed by the regeneration reaction. While this may sufficiently regenerate the filter, oxygen stored in the exhaust system (e.g., in a catalyst washcoat) may be depleted and cannot be replenished due to the complete consumption of excess oxygen during the regeneration reaction. In this case, passive filter regeneration cannot be performed without supplying excess oxygen via other means.
One approach that at least partially addresses the above issues includes a method for an emission control device including a catalyst and a filter, comprising passively regenerating the filter, and adjusting, via a controller, a duration of active regeneration of the filter based on an oxygen storage capacity of the emission control device.
In a more specific example, the method further comprises determining an amount of particulate matter stored in the filter, and actively regenerating the filter if the amount of particulate matter is greater than or equal to a threshold.
In another example, active regeneration of the filter includes initiating deceleration fuel shut-off.
In yet another example, the method further comprises extending a duration of deceleration fuel shut-off to replenish at least a portion of oxygen stored in the emission control device.
In this way, DFSO initiated as part of active filter regeneration may be utilized to replenish oxygen stored in the emission control device, which may increase the frequency with which passive filter regeneration may be performed. Consequently, the frequency with which engine operation is modified to supply excess oxygen for filter regeneration may be reduced, which may increase fuel economy and vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Finally, the above explanation does not admit any of the information or problems were well known.